Finished a long run this weekend and took the time to fill the DEF passing through Dodge City, KS at the Flying J. Now that I've filled it I have a bit more information. First, the DEF tank wasn't completely full when the truck was delivered. On my gauge, when the tank is full, the needle lines up exactly with the full line on the gauge, it was a bit below that when delivered. When I filled the tank yesterday the gauge was almost exactly in the middle of the red portion, showing about 1/8 tank. I put 7.1 gallons of DEF in the tank. Milage on the truck was just over 4700 miles. I've heard two stories here about the DEF tank capacity. Some say its 11 gallons, my understanding is its 8 gallons, which is right? Most of us are still in low milage use, I'm wondering if anyone has seen the warning message of the DEF being low and how much it took to refill the DEF tank? No complaining, its not a factor in cost of maintenance, just curious.